Xiaolin, Opal, Mako, and Bolin stared at Korra and Heylin, who were having some sort of stare down.

Opal: What are they waiting for?

Xiaolin: They're waiting for the other to make the first move.

Bolin: What should we call Korra now? RaaKorra maybe.

Xiaolin, Opal, and Mako stared at Bolin.

Mako: Really? That's your big problem?

Bolin: Yeah, too stupid, got it.

The group focused their attention on Korra and Heylin. After a few more seconds, Heylin used his enhanced speed to move from different spots to charge at Korra. Instead of getting out of the way, Korra stood her ground; when she was within Heylin's striking distance, she deflected it, breaking Heylin's balance, and then she blasted him back with an energy blast that sent him crashing into an ice cropping. Korra then charged at him and fired blue fire balls at Heylin; each one made its mark upon him. When she got closer, Korra jumped into the air and used her airbending to increase her descent and slammed a fist into Heylin's gut.

Heylin: (Coughs) Get..off...ME!

Heylin brought his right hand to Korra's face and blasted her off him. She slid across the ground, but she got up and shook it off. Heylin saw that he was outmatched at this point and decided he needed to give himself an energy boost to save himself. He started to gather energy, causing a red glow to come on him, signaling what he was doing.

Xiaolin: (Sees what Heylin's doing) Heylin, stop! You don't know what more energy could do to you!

Heylin: I don't take orders from you, Cousin.

As he gathered the energy, he began to fall over and started to feel pain.

Heylin: (Turns reddish-black like Vaatu) What's...happening...to me?!

Xiaolin: What I warned you about! With the amount of energy you have and the minds of the spirits you absorbed, it is causing increased brainwave activity in your mind and theirs. Your mind and theirs are being merged and will become the mind of a reckless and impulsive animal!

Heylin transformed into a reddish-black Dark Spirit; his legs became reptile like, his tail's length increased and lost its devil traits, his face turned into that of a monster, his teeth became sharper, and his horns started to curve upward. After the energy boost was done, he roared like an animal and stood on all fours, and charged at Korra. He hit Korra back with his horns, and did so again, and again, and again, and again. When he tried to hit Korra again, she thrust her hands into the ground and caused spirit vines to emerge from the ground and entangle Heylin. Korra got up and Heylin broke free from the vines. Korra then used lavabending to create a ring of lava around Heylin. Heylin stood on his legs and flew into the air, but Korra shot the lava into the air and brought it down on Heylin, causing him to crash into the ground. Korra then cooled the lava to trap Heylin, but he broke out of it and shot a purple energy beam from his mouth at Korra. She created an earth wall to block the beam; the wall exploded as a result, and he charged through the dust and punched Korra. Korra staggered back as a result, and Heylin then tail swept her legs, causing her to fall onto her back. Heylin morphed his right arm into needle and tried to stab Korra with it, but she rolled out of the way with her back facing Heylin, and she then hit him by thrusting the tentacles on her back, causing him to go up into the air and crash back onto the ground. When he got up, he fired another mouth beam at Korra, but she energybended it right back at him; he staggered from the blast he took, and then Korra shot a blue energy beam from the eye of the Raava symbol on her at Heylin, knocking him out. Korra took the opportunity and began to spiritbend him; he turned gold from the purification and started to dissipate, and from his dissipation, thousands of blue orbs emerged.

Xiaolin: (Looks in awe with the others) The souls he absorbed. They are free now.

Opal: What will happen to them?

Xiaolin: If any of them were separated from their bodies for a time shorter than twenty-four hours, they will return to their body. If not, then they will go on into the afterlife.

The bubble around the group disappeared and one soul entered Tonraq's body, bringing him back. He started to get up as a result.

Mako: Chief Tonraq.

The group goes to Tonraq's side.

Bolin: You okay?

Tonraq: I'm fine. But where's Korra?

Xiaolin pointed to her; when the group looked at her, she began to turn back to normal. After the transformation was done, Korra looked at her father with tears in her eyes and a smile on her face and ran toward him.

Korra: (Hugs Tonraq) Dad!

Tonraq: I knew you could do it, Korra.

Bolin: So what was it like being eaten by an evil Dark Spirit?

Opal: Bolin!

Bolin: I'm sorry!

Tonraq: (Stops hugging Korra) It's okay. I felt darkness all around me, but then I felt a light pulling me out of it. (Looks at Korra) Thank you, Korra.

Korra: Just doing what I knew was right.

Republic City, four days later

The group returned to Republic City to celebrate and tell everyone what had happened. The celebration occurred on Air Temple Island. Mako and Asami were talking to Lin and President Raiko about what happened. Opal was reporting the journey to Tenzin and Jinora. Bolin was telling Varrick, Zhu Li, Ikki, Meelo, and Rohan the battle between Korra and Heylin.

Bolin: (Raises his arms up) ...and then after bending the energy blast right back at him, Korra shot him with her own energy blast right at him!

Rohan: Cool!

Ikki: Nice.

Meelo: Wish I saw it in person.

Varrick: This could be perfect for my next mover.

Zhu Li: (Puts her hand on Varrick's shoulder) Easy, Varrick. You're at a party after all.

Varrick: Right. Best not to get caught up in work at these things.

Korra saw Xiaolin sitting on the stairs in front of the island's gate looking at the spirit portal as it lit up the night sky. She sat right next to him.

Korra: Not big on parties?

Xiaolin: I've never been to one. Avatar Wan tried to get me to come to one, but I refused. I was more focused on looking for the rest of the Pure Dark Spirits.

Korra: Well, they're all gone now. Any idea if the Red Lotus might show up?

Xiaolin: After Heylin's betrayal, I would imagine that most of them and their leaders would have had their souls taken. And I would imagine that their bodies would have all turned to dust if he did start this after we killed Phobos and Parasite. So, I would say no.

Korra: Are you gonna leave?

Xiaolin: I was gonna do that after we had finished defeating Heylin. But, after the two of us had become a couple, I learned something.

Korra: What?

Xiaolin: I don't want to leave you.

Korra: (Smiles) Is that a wedding proposal?

Xiaolin: (Smiles) If you want it to be?

Korra: Here's my answer.

Korra kissed Xiaolin on the lips and they both hugged each other as well.

The End.

Trivia

I originally wanted to turn Heylin into a giant monster. This would've been caused by a fight between him and Korra in the Spirit World when he fires an energy beam at Korra and she uses the Avatar State to fire her own at it, causing a black hole to open up sucking in Heylin and several Dark Spirits. When the black hole disappears, everyone thinks it's over, and then Heylin tears his way out of the dimension he got sent to, having been forcefully fused with all the Dark Spirits that got sent with him. He would then release an energy wave that goes through the North and South Spirit Portals and steals the souls of everyone in the Northern and Southern Water Tribes. Xiaolin created a barrier to protect Korra, Bolin, Mako, and Opal, the barriers residual strength made Heylin think that they are spirits, and he heads to the Fog of Lost Souls to consume the souls there. The group learns that he is following the closest concentrations of souls and that he'll go to Republic City after he's done with the fog. Korra would then tap into even greater amounts of power in the Avatar State and turn into the fusion of her and Raava I used but as a giant, like UnaVaatu.